The recent introduction of the FTTH (Fiber to the Home) system has enabled the use of optical fibers for wiring in the general household appliances, and thus the demand on optical communication has significantly increased. As a transmission mode to cope with the increased demand, wavelength division multiplex (WDM) has been introduced. WDM is a communication mode in which one optical fiber transmits signals of multiple wavelengths, and in association with the introduction of this system, there is an increasing demand on an optical fiber ribbon with multi-fibers, such as optical fiber ribbons with 4 fibers, 8 fibers, 12 fibers, 16 fibers, 24 fibers, 32 fibers and the like.
Under such circumstances, the optical fiber ribbon found uses in indoor wiring, or internal wiring in devices. For this reason, the demand on the flame-retardant optical fiber ribbon is ever increasing in order to prevent combustion of the fibers on fire.
As one form of such optical fiber ribbons with multi-fibers, interest has been attracted by an optical fiber ribbon which achieves a thin type multi-fiber structure.
A conventional tape code is formed such that in the periphery of a plurality of coated optical fibers 2 disposed in a row in plane as shown in FIG. 22(A), an optional anti-tension body k which is a reinforcing fiber, etc. is disposed as shown in FIG. 22(B), and the periphery of optional anti-tension body k is coated with a polyvinyl chloride (PVC) resin composition 16.
For a method for flame-retardation in an optical fiber ribbon, there can be mentioned a method in which a flame-retardant material is used in the coating for a coated optical fiber per se, and a method in which the structure of a coated optical fiber itself is retained as is and its periphery is coated with a flame-retardant material.
However, disadvantages are found in any of such methods. In the former method, although the flame-retardancy is imparted to the coating material for a coated optical fiber, the flame-retardant materials in general are poor in light transmission. For example, a conventional optical fiber ribbon is, in many cases, formed and coated with a UV-curable resin which is a non-flame retardant material, but when a flame-retardant is added to this UV-curable resin, UV transmission is reduced, thus making it difficult to cure the UV-curable resin.
For this reason, such UV-curable resins that are widely used in the coating material for a coated optical fiber cannot be used, and thus reduction in productivity is unavoidable.
Meanwhile, in the latter method, since the structure of a coated optical fiber itself is retained as is, the dimension of tape code is enlarged and thus it is inappropriate for wiring into the narrow sites such as internal wiring in devices.
The situation also applies to an optical fiber ribbon (a ribbon-type optical fiber).
An optical fiber ribbon in general has a structure in which a plurality of optical fibers are arranged in parallel, and their peripheries are all coated with a coating layer (a tape layer).
In the case where this optical fiber ribbon is to be made flame-retardant, the following methods can be taken into consideration: a method in which a flame-retardant material is used in the coating for a coated optical fiber or in the tape layer in the same manner as for a coated optical fiber; and a method in which the structure of the optical fiber ribbon itself is retained as it is, and its periphery is coated with a flame-retardant material.
In this case, too, for the same reason given for a coated optical fiber, addition of a flame-retardant, for example, to a coating made of a UV-curable resin, for the purpose of flame-retardancy as described for the structure in the former method, results in reduction of UV transmission, thus making it difficult to cure the UV-curable resin.
Further, in the latter case, coating with a flame-retardant material leads to a larger thickness, and an adverse effect thereof on miniaturization or micronization of devices is unavoidable.
Additionally, in the case of such an optical fiber ribbon, since it often occurs that signal transmission is individually achieved in each of the fibers, it has been necessary to make a measurement after extracting one particular fiber, or to carry out branch wiring from an aerial cable, for example.
This step of separating single fiber is carried out such that the resin coating is torn off and the optical fibers are extracted one by one, requiring very delicate manual operation. Further, since the resin attached around the optical fibers after separation is in the form of being finely divided, it is very difficult to remove the resin completely, thus lowering workability.
Moreover, in the middle of the course of communication, when a coated optical fiber is extracted by carrying out the separation of single fiber from the above-mentioned optical fiber ribbon, stress applied to the coated optical fiber may lead to loss of transmission and thus to possible cut-off in communication.
The object of the present invention is to provide a thin type, flame-retardant optical fiber ribbon.
Another object of the present invention is to provide an optical fiber ribbon for easy separation of single fiber.
Another object of the present invention is to provide a method of manufacturing the optical fiber ribbon with easy workability and high reliability.